What is the difference between weather and climate?

Weather is the state of the atmosphere at a particular time and place. Climate is the statistical description of weather over a long period, conventionally thirty years, for a given region.

The often-quoted summary is that climate is what you expect and weather is what you get. A more precise framing is that climate describes the distribution, including averages, extremes and variability, while weather is a single sample drawn from it.

The distinction matters because of a common reasoning error in both directions. A single cold spell says nothing about climate, in the same way one tall person says nothing about average height. Equally, a single hot day is not evidence of climate change on its own. What is meaningful is a shift in the distribution: changes in the frequency of extremes, in seasonal timing, in long-run averages.

The difference also explains a genuine asymmetry in prediction. Weather forecasting degrades rapidly beyond about a week because the atmosphere is chaotic, meaning tiny differences in initial conditions grow quickly. Climate projection is a different kind of problem: it does not attempt to say what a particular day will be like, only how the statistics behave under given conditions. That is why it can be meaningful over decades while a fortnight forecast is not.

An analogy that holds well is a dice roll. Predicting the next roll is hard. Predicting that a thousand rolls will average around three and a half is straightforward, and remains so even though each individual roll is unpredictable.

Regional climate is also more than temperature, encompassing rainfall patterns, humidity, wind and seasonality.